Foreign substance detection method for wireless charging and apparatus therefor

ABSTRACT

The present invention relates to a foreign substance detection method, and an apparatus and a system therefor. A foreign substance detection method in a wireless power transmitter, according to an embodiment of the present invention, may comprise the steps of: if an object placed in a charging area is detected, searching for a current peak frequency with a maximum quality factor value in an available frequency band; receiving, from a wireless power receiver, a foreign substance detection state packet including a reference peak frequency; determining a foreign substance detection reference frequency on the basis of the reference peak frequency; and determining whether or not a foreign substance is present by comparing the current peak frequency with the foreign substance detection reference frequency. Therefore, the present invention has an advantage of being capable of detecting a foreign substance more effectively and accurately.

TECHNICAL FIELD

Embodiments relate to wireless power transmission technology and, moreparticularly, to a method of detecting a foreign object placed in acharging area of a wireless power transmitter, and an apparatustherefor.

BACKGROUND ART

Recently, as information and communication technology has been rapidlydeveloped, a ubiquitous society based on information and communicationtechnology is being developed.

In order to connect information communication devices anytime andanywhere, sensors equipped with a computer chip having a communicationfunction should be installed in all social facilities. Accordingly,supplying power to such devices or sensors is a new challenge. Inaddition, as the types of mobile devices such as music players such asBluetooth handsets or iPods as well as mobile phones have rapidlyincreased, it is necessary for users to take more time and effort tocharge batteries. As a method of solving such problems, wireless powertransmission technology has recently attracted attention.

Wireless power transmission or wireless energy transfer refers totechnology for wirelessly transmitting electric energy from atransmitter to a receiver using the magnetic induction principle. In the1800s, electric motors or transformers using the electromagneticinduction principle began to be used and, thereafter, attempts have beenmade to radiate electromagnetic waves such as high-frequency waves,microwaves and lasers to transfer electric energy. Frequently usedelectric toothbrushes and some electric shavers are charged using theelectromagnetic induction principle.

Up to now, wireless energy transfer methods may be broadly divided intomagnetic induction, electromagnetic resonance and radio frequency (RF)transmission of a short-wavelength radio frequency.

The magnetic induction method uses a phenomenon that, when two coils arelocated adjacent to each other and then current is applied to one coil,a magnetic flux is generated to cause an electromotive force in theother coil, and is rapidly being commercialized in small devices such asmobile phones. The magnetic induction method may transfer power of up toseveral hundred kilowatts (kW) and has high efficiency. However, since amaximum transmission distance is 1 centimeter (cm) or less, a device tobe charged should be located adjacent to a charger or the floor.

The electromagnetic resonance method uses an electric field or amagnetic field instead of using electromagnetic waves or current. Theelectromagnetic resonance method is rarely influenced by electromagneticwaves and thus is advantageously safe for other electronic devices andhuman. In contrast, this method may be used in a limited distance andspace and energy transmission efficiency is somewhat low.

The short-wavelength wireless power transmission method (brieflyreferred to as the RF transmission method) takes advantage of the factthat energy may be directly transmitted and received in the form ofradio waves. This technology is an RF wireless power transmission methodusing a rectenna. A rectenna is a combination of an antenna and arectifier and means an element for directly converting RF power into DCpower. That is, the RF method is technology for converting AC radiowaves into DC. Recently, as efficiency of the RF method has beenimproved, studies into commercialization of the RF method have beenactively conducted

Wireless power transmission technology may be used not only in mobilerelated industries but also in various industries such as IT, railroadsand home appliances.

If a conductor which is not a wireless power receiver, that is, aforeign object (FO), is present in a wireless charging area, anelectromagnetic signal received from a wireless power transmitter may beinduced in the FO, thereby increasing in temperature. For example, theFO may include coins, clips, pins, and ballpoint pens.

If an FO is present between a wireless power receiver and a wirelesspower transmitter, wireless charging efficiency may be significantlylowered, and the temperatures of the wireless power receiver and thewireless power transmitter may increase due to increase in ambienttemperature of the FO. If the FO located in the charging area is notremoved, power waste may occur and the wireless power transmitter andthe wireless power receiver may be damaged due to overheating.

Accordingly, accurate detection of the FO located in the charging areais becoming an important issue in wireless charging technology.

In the related art, a method of determining whether an FO is presentbased on a threshold value determined based on a reference qualityfactor value and a measured quality factor value and a method ofdetermining whether an FO is present on a wireless power transmissionpath based on wireless power path loss were disclosed. However, thesemethods have FO detection accuracy which deteriorates according to thetype of a receiver and a transmitter.

DISCLOSURE Technical Problem

Embodiments provide a foreign object detection method for wirelesscharging and an apparatus and system therefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by comparing a current peakfrequency with a foreign object reference frequency (frequency boundaryvalue) determined based on a reference peak frequency, and an apparatustherefor.

Embodiments provide a foreign object detection method capable of moreaccurately detecting a foreign object, by determining whether a foreignobject is present based on statistical data of a communication errorcount as well as peak frequency change, and an apparatus and systemtherefor.

The technical problems solved by the embodiments are not limited to theabove technical problems and other technical problems which are notdescribed herein will become apparent to those skilled in the art fromthe following description.

Technical Solution

Embodiments provide a foreign object detection method, and an apparatustherefor.

A foreign object detection method of a wireless power transmitteraccording to an embodiment may include searching for a current peakfrequency having a maximum quality factor value within an availablefrequency band when an object placed in a charging area is detected,receiving a foreign object detection status packet including a referencepeak frequency from a wireless power receiver, determining a foreignobject detection reference frequency based on the reference peakfrequency, and comparing the current peak frequency with the foreignobject detection reference frequency to determine whether a foreignobject is present.

Here, the determining of the foreign object detection referencefrequency may include determining a tolerance and determining theforeign object detection reference frequency by a sum of the referencepeak frequency and the tolerance.

For example, the tolerance may be determined based on peak frequencychange according to movement of a receiver in the charging area.

In another example, the tolerance may be determined based on peakfrequency change according to a difference between types of wirelesspower transmitters.

In another example, the tolerance may be determined based on the largervalue of maximum peak frequency change according to movement of areceiver in the charging area and maximum peak frequency changeaccording to a difference between types of wireless power transmitters.

In addition, when the current peak frequency is greater than the foreignobject detection reference frequency, it may be determined that theforeign object is present.

In addition, the current peak frequency may be searched after powertransfer is temporarily stopped before entering a ping phase foridentifying the wireless power receiver.

In addition, the reference peak frequency may have a maximum qualityfactor value within an available frequency band in a state in which onlythe wireless power receiver is placed in the charging area.

In addition, the foreign object detection method may further includeending power transfer to the wireless power receiver and enteringselection phase upon determining that the foreign object is detected.

In addition, the foreign object detection method may further includeoutputting a predetermined warning alarm indicating that the foreignobject has been detected after ending power transfer.

In addition, the foreign object detection status packet may furtherinclude mode information, and the reference peak frequency included inthe foreign object detection status packet may be identified based onthe mode information.

A foreign object detection method of a wireless power transmitteraccording to another embodiment may include searching for a current peakfrequency having a maximum quality factor value within an availablefrequency band when an object placed in a charging area is detected,collecting statistical data of a communication error count, determininga foreign object detection reference frequency based on a reference peakfrequency when a foreign object detection status packet including thereference peak frequency is received from a wireless power receiver,comparing the current peak frequency with the foreign object detectionreference frequency, determining whether the communication error countexceeds a predetermined communication error reference value when thecurrent peak frequency is greater than the foreign object detectionreference frequency as the result of comparison, and determining that aforeign object is present upon determining that the communication errorcount exceeds the predetermined communication error reference value.

Here, the statistical data of the communication error count may becollected in at least one of a ping phase or an identification andconfiguration phase.

In addition, the communication error count may be calculated based on atleast one of the number of reception failures of a response signal to apower signal transmitted to identify a wireless power receiver in theping phase and the number of reception failures of an identificationpacket and a configuration packet in the identification andconfiguration phase.

Here, the determining of the foreign object detection referencefrequency may include determining a tolerance and determining theforeign object detection reference frequency by a sum of the referencepeak frequency and the tolerance.

For example, the tolerance may be determined based on peak frequencychange according to movement of a receiver in the charging area.

In another example, the tolerance may be determined based on peakfrequency change according to a difference between types of wirelesspower transmitters.

In another example, the tolerance may be determined based on the largervalue of maximum peak frequency change according to movement of areceiver in the charging area and maximum peak frequency changeaccording to a difference between types of wireless power transmitters.

A foreign object detection apparatus for detecting a foreign objectplaced in a charging area according to an embodiment may include asearch unit configured to search for a current peak frequency having amaximum quality factor value within an available frequency band when anobject placed in a charging area is detected, a communication unitconfigured to receive a foreign object detection status packet includinga reference peak frequency from a wireless power receiver, adetermination unit configured to determine a foreign object detectionreference frequency based on the reference peak frequency, and adetection unit configured to compare the current peak frequency with theforeign object detection reference frequency to detect a foreign object.

Here, the determination unit may determine the foreign object detectionreference frequency by a sum of the reference peak frequency and atolerance.

For example, the tolerance may be determined based on peak frequencychange according to movement of a receiver in the charging area.

In another example, the tolerance may be determined based on peakfrequency change according to a difference between types of wirelesspower transmitters.

In another example, the tolerance may be determined based on the largervalue of maximum peak frequency change according to movement of areceiver in the charging area and maximum peak frequency changeaccording to a difference between types of wireless power transmitters.

In addition, when the current peak frequency is greater than the foreignobject detection reference frequency, the detection unit may determinethat the foreign object is present.

In addition, the search unit may search for the current peak frequencyafter power transfer is temporarily stopped before entering a ping phasefor identifying the wireless power receiver.

In addition, the reference peak frequency may have a maximum qualityfactor value within an available frequency band in a state in which onlythe wireless power receiver is placed in the charging area.

In addition, the foreign object detection apparatus may further includean alarm unit configured to output a predetermined warning alarmindicating that the foreign object has been detected when the foreignobject is detected by the detection unit.

A foreign object detection apparatus for detecting a foreign objectplaced in a charging area according to another embodiment may include asearch unit configured to search for a current peak frequency having amaximum quality factor value within an available frequency band when anobject placed in a charging area is detected, a communication unitconfigured to receive a packet from a wireless power receiver, acontroller configured to monitor a reception status of the packet tocollect statistical data of a communication error count, and adetermination unit configured to determine a foreign object detectionreference frequency based on a reference peak frequency when a foreignobject detection status packet including the reference peak frequency isreceived, comparing the current peak frequency with the foreign objectdetection reference frequency. The controller may determine a foreignobject is present, when the current peak frequency is greater than theforeign object detection reference frequency and the communication errorcount exceeds a predetermined communication error reference value.

The control unit or controller 1180 according to an embodiment may beintegrated with the communication unit 1160. If the wireless powertransmitter and the wireless power receiver perform in-bandcommunication, the controller 1180 may demodulate a signal using currentor a voltage of the coil unit 1130.

A foreign object detection apparatus according to an embodiment includesa coil unit including an inductor and a resonant capacitor andconfigured to convert current into flux of magnetic force, an inverterconfigured to receive and convert direct current (DC) power intoalternating current (AC) power and to transmit the AC power to the coilunit, and a controller configured to control a frequency of the AC poweroutput from the inverter and to demodulate a signal using a voltage orcurrent of the coil unit. The controller may be configured to detect anobject placed in the charging area to measure a peak frequency having amaximum quality factor value, to receive a foreign object detectionstatus packet including a reference peak frequency from a wireless powerreceiver, to determine a frequency for detecting a foreign object basedon the reference peak frequency, and to compare the peak frequency withthe determined frequency to determine whether a foreign object ispresent.

In addition, the controller may determine the frequency for detectingthe foreign object by a sum of the reference peak frequency and atolerance.

The controller may measure the peak frequency before the wireless powerreceiver receives a ping signal.

The reference peak frequency may correspond to a maximum quality factorvalue within an available frequency band in a state in which only thewireless power receiver is placed in the charging area.

Another embodiment provides a computer-readable recording medium havingrecorded thereon a program for performing any one of the foreign objectdetection methods.

The aspects of the disclosure are only a part of the preferredembodiments of the disclosure, and various embodiments based ontechnical features of the disclosure may be devised and understood bythe person having ordinary skill in the art based on the detaileddescription of the disclosure.

Advantageous Effects

The effects of the method, apparatus and system according to embodimentsare as follows.

Embodiments have an advantage of providing a method of detecting aforeign object for wireless charging and an apparatus and systemtherefor.

Embodiments have an advantage of providing a method of detecting aforeign object, which is capable of more accurately detecting a foreignobject and an apparatus and system therefor.

Embodiments have an advantage of providing a wireless power transmittercapable of minimizing unnecessary power waste and a heating phenomenondue to a foreign object.

Embodiments have an advantage of providing a foreign object detectionmethod capable of more accurately detecting a foreign object, bycomparing a current peak frequency with a foreign object referencefrequency (frequency boundary value) determined based on a referencepeak frequency and an apparatus therefor.

Embodiments have an advantage of providing a foreign object detectionmethod capable of more accurately detecting a foreign object, bydetermining whether a foreign object is present based on statisticaldata of a communication error count as well as peak frequency change andan apparatus therefor.

Embodiments have an advantage of accurately detecting a foreign objectregardless of movement of a receiver in a charging area and the type ofa transmitter.

The effects of the disclosure are not limited to the above-describedeffects and other effects which are not described herein may be derivedby those skilled in the art from the following description of theembodiments of the disclosure. That is, effects which are not intendedby the disclosure may be derived by those skilled in the art from theembodiments of the disclosure.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment.

FIG. 2 is a state transition diagram explaining a wireless powertransfer procedure according to an embodiment.

FIG. 3 is a block diagram illustrating the structure of a wireless powerreceiver according to an embodiment.

FIG. 3 is a diagram illustrating a packet format according to anembodiment.

FIG. 4 is a diagram illustrating a packet format according to anembodiment.

FIG. 5 is a diagram illustrating types of packets according to anembodiment.

FIG. 6 is a block diagram illustrating the configuration of a foreignobject detection apparatus according to an embodiment.

FIG. 7 is a block diagram illustrating the configuration of a foreignobject detection apparatus according to another embodiment.

FIG. 8 is a state transition diagram illustrating a foreign objectdetection procedure of a foreign object detection apparatus according toan embodiment.

FIG. 9 is a state transition diagram illustrating a foreign objectdetection procedure of a foreign object detection apparatus according toanother embodiment.

FIG. 10 is a view illustrating a foreign object detection status packetmessage according to an embodiment.

FIG. 11 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to an embodiment.

FIG. 12 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to another embodiment.

FIG. 13 is an experimental result table illustrating change in qualityfactor value and peak frequency according to placement of a foreignobject in a wireless charging system according to an embodiment.

FIG. 14 is an experimental result table illustrating a peak frequency ofeach receiver type and change in peak frequency according to placementof a foreign object according to an embodiment.

FIG. 15 is an experimental result table illustrating change in qualityfactor value and peak frequency according to movement of a wirelesspower receiver.

FIG. 16 is an experimental result showing change in peak frequencyaccording to the type of a wireless power transmitter andpresence/absence of a foreign object.

FIG. 17 is a graph illustrating change in quality factor value measuredwhen a resonant frequency of a coil of a wireless power transmitteraccording to an embodiment is 100 kHz and a wireless power receiver or aforeign object is placed in a charging area.

BEST MODE

A foreign object detection method of a wireless power transmitteraccording to an embodiment may include searching for a current peakfrequency having a maximum quality factor value within an availablefrequency band when an object placed in a charging area is detected,receiving a foreign object detection status packet including a referencepeak frequency from a wireless power receiver, determining a foreignobject detection reference frequency based on the reference peakfrequency, and comparing the current peak frequency with the foreignobject detection reference frequency to determine whether a foreignobject is present.

MODE FOR INVENTION

Hereinafter, apparatuses and various methods according to embodimentswill be described in detail with reference to the accompanying drawings.In general, a suffix such as “module” or “unit” may be used to refer toelements or components. Use of such a suffix herein is merely intendedto facilitate description of the specification, and the suffix itself isnot intended to have any special meaning or function.

In the following description of the embodiments, it will be understoodthat, when each element is referred to as being formed “on” or “under”the other element, it can be directly “on” or “under” the other elementor be indirectly formed with one or more intervening elementstherebetween. In addition, it will also be understood that “on” or“under” the element may mean an upward direction and a downwarddirection of the element.

In the description of embodiments, an apparatus having a function fortransmitting wireless power in a wireless charging system may be usedinterchangeably with a wireless power transmitter, a wireless powertransfer apparatus, a wireless electric power transfer apparatus, awireless electric power transmitter, a transmission end, a transmitter,a transmission apparatus, a transmission side, a wireless power transferapparatus, a wireless power transferor, etc., for convenience ofdescription. An apparatus having a function for receiving wireless powerfrom a wireless power transfer apparatus may be used interchangeablywith a wireless electric power reception apparatus, a wireless electricpower receiver, a wireless power reception apparatus, a wireless powerreceiver, a reception terminal, a reception side, a reception apparatus,a receiver, etc.

The transmitter according to embodiment may be configured in the form ofa pad, a cradle, an access point (AP), a small base station, a stand, aceiling embedded structure or a wall-mounted structure. One transmittermay transfer power to a plurality of wireless power receptionapparatuses. To this end, the transmitter may include at least onewireless power transfer means. Here, the wireless power transfer meansmay use various wireless power transfer standards based on anelectromagnetic induction method of performing charging using theelectromagnetic induction principle in which a magnetic field isgenerated in a power transfer-end coil and electricity is induced in areception-end coil by the magnetic field. Here, the wireless powertransfer means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

In addition, a receiver according to an embodiment may include at leastone wireless power reception means and may simultaneously receivewireless power from two or more transmitters. Here, the wireless powerreception means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

The receiver according to the embodiment may be used in a smallelectronic apparatus such as a mobile phone, a smartphone, a laptop, adigital broadcast terminal, a personal digital assistant (PDA), aportable multimedia player (PMP), a navigation system, an MP3 player, anelectric toothbrush, an electronic tag, a lighting device, a remotecontroller, a fishing float, a wearable device such as a smart watch,etc. without being limited thereto, and may be used in any apparatusincluding wireless power reception means according to embodiment tocharge a battery.

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment.

Referring to FIG. 1, the wireless charging system roughly includes awireless power transfer end 10 for wirelessly transmitting power, awireless power reception end 20 for receiving the transmitted power andan electronic apparatus 30 for receiving the received power.

For example, the wireless power transfer end 10 and the wireless powerreception end 20 may perform in-band communication in which informationis exchanged using the same frequency band as the operating frequencyused for wireless power transfer.

In in-band communication, when a power signal 41 transmitted by thewireless power transfer end 10 is received by the wireless powerreception end 20, the wireless power reception end 20 may modulate thereceived power signal and transmit a modulated signal 42 to the wirelesspower transfer end 10.

In another example, the wireless power transfer end 10 and the wirelesspower reception end 20 may perform out-of-band communication in whichinformation is exchanged using the frequency band different from theoperating frequency used for wireless power transfer.

For example, the information exchanged between the wireless powertransfer end 10 and the wireless power reception end 20 may includestatus information of each other and control information. Here, thestatus information and the control information exchanged between thetransmission end and the reception end will become more apparent throughthe following description of the embodiments.

In-band communication and out-of-communication may provide bidirectionalcommunication, but the embodiments are not limited thereto. In anotherembodiment, in-band communication and out-of-communication may provide aunidirectional communication or half duplex communication.

For example, unidirectional communication may, but is not limited to,mean transmission of information from the wireless power reception end20 to the wireless power transfer end 10 or transmission from thewireless power transfer end 10 to the wireless power reception end 20.

The half duplex communication method is characterized in thatbidirectional communication between the wireless power reception end 20and the wireless power transfer end 10 is enabled but information can betransmitted only by one device at a certain point in time.

The wireless power reception end 20 according to the embodiment mayacquire a variety of status information of the electronic apparatus 30.For example, the status information of the electronic apparatus 30 mayinclude, but is not limited to, current power usage information, currentpower usage information, information for identifying an executedapplication, CPU usage information, battery charge status information,battery output voltage/current information, etc. and may includeinformation capable of being acquired from the electronic apparatus 30and being used for wireless power control.

In particular, the wireless power transfer end 10 according to theembodiment may transmit a predetermined packet indicating whether fastcharging is supported to the wireless power reception end 20. Thewireless power reception end 20 may inform the electronic apparatus 30that the wireless power transfer end 10 supports the fast charging mode,upon determining that the wireless power transfer end 10 supports thefast charging mode. The electronic apparatus 30 may display informationindicating that fast charging is possible through a predetermineddisplay means, for example, a liquid crystal display.

FIG. 2 is a state transition diagram explaining a wireless powertransfer procedure.

Referring to FIG. 2, power transfer from the transmitter to the receiveraccording to the embodiment may be broadly divided into a selectionphase 510, a ping phase 520, an identification and configuration phase530, a negotiation phase 540, a calibration phase 550, a power transferphase 560 and a renegotiation phase 570.

The selection phase 510 may transition when power transfer starts orwhen a specific error or a specific event is sensed while power transferis maintained (for example, including reference numerals S502, S504,S508, S510 and S512). The specific error and the specific event willbecome apparent from the following description. In addition, in theselection phase 510, the transmitter may monitor whether an object ispresent on an interface surface. Upon detecting that the object ispresent on the interface surface, the transmitter may transition to theping phase 520. In the selection phase 510, the transmitter may transmitan analog ping signal having a very short pulse and detect whether anobject is present in an active area of the interface surface based onchange in current of a transmission coil or a primary coil.

If the object is detected in the selection phase 510, the wireless powertransmitter may measure the quality factor of a wireless power resonantcircuit (e.g., a power transfer coil and/or a resonant capacitor).

In one embodiment, when the object is detected in the selection phase510, the quality factor may be measured in order to determine whetherthe wireless power receiver is placed in the charging area along with aforeign object.

The coil provided in the wireless power transmitter has an inductanceand/or a series resistance component in the coil which may decrease dueto environmental change, thereby decreasing the quality factor value. Inorder to determine whether the foreign object is present using themeasured quality factor value, the wireless power transmitter mayreceive, from the wireless power receiver, a reference quality factorvalue previously measured in a state in which a foreign object is notplaced in the charging area.

The reference quality factor value received in the negotiation phase 540may be compared with the measured quality factor value, therebydetermining whether the foreign object is present. However, in the caseof a wireless power receiver having a low reference quality factor (forexample, a specific wireless receiver may have a low reference qualityfactor value according to the type, usage and characteristics of thewireless power receiver), since a difference between the quality factorvalue measured when the foreign object is present and the referencequality factor is small, it is difficult to determine whether a foreignobject is present. Accordingly, it is necessary to further considerother determination elements or to determine whether a foreign object ispresent using other methods.

In another embodiment, when the object is detected in the selectionphase 510, the quality factor value within a specific frequency region(e.g., an operating frequency region) may be measured in order todetermine whether the wireless power receiver is placed in the chargingarea along with the foreign object. The coil of the wireless powertransmitter may have the inductance and/or series resistance componentin the coil which may decrease due to environmental change, therebychanging (shifting) the resonant frequency of the coil of the wirelesspower transmitter. That is, a quality factor peak frequency as afrequency at which the maximum quality factor value is measured in theoperating frequency band may be shifted.

For example, since the wireless power receiver includes a magneticshield (shielding material) having high permeability, the highpermeability may increase the inductance value measured in the coil ofthe wireless power transmitter. In contrast, a foreign object, which isa metallic material, decreases the inductance value.

FIG. 18 is a graph showing change in quality factor value measured whenthe wireless power receiver or the foreign object is placed in thecharging area in the case where the resonant frequency of the coil ofthe wireless power transmitter according to an embodiment is 100 kHz.

Generally, in the case of an LC resonant circuit, the resonant frequencyf_resonant is calculated by

$\frac{1}{2\; \pi \sqrt{LC}}.$

Referring to the left graph of FIG. 18, when only the wireless powerreceiver is placed in the charging area, since the L value increases,the resonant frequency decreases to be moved (shifted) to the left onthe frequency axis.

Referring to the right graph of FIG. 18, when a foreign object is placedin the charging area, since the L value decreases, the resonantfrequency increases to be moved (shifted) to the right on the frequencyaxis.

In order to determine whether a foreign object is present using afrequency at which a maximum quality factor is measured, that is, ameasured peak frequency, the wireless power transmitter may receive thereference maximum quality factor frequency pre-measured in a state inwhich the foreign object is not placed in the charging area, that is,the reference peak frequency, from the wireless power receiver. Thereceived reference peak frequency value may be compared with themeasured peak frequency value in the negotiation phase 540, therebydetermining whether a foreign object is present.

The foreign object detection through peak frequency comparison may beused along with a method of comparing quality factor values. If adifference between the reference quality factor value and the measuredquality factor value is small, for example, if the difference is equalto or less than 10%, presence of the foreign object may be determined bycomparing the reference peak frequency with the measured peak frequency.In contrast, if the difference between the quality factors exceeds 10%,the wireless power transmitter may immediately determine that theforeign object is present.

In another example, upon determining that the foreign object is notpresent as the result of comparing the reference quality factor valuewith the measured quality factor value, the reference peak frequency maybe compared with the measured peak frequency to determine whether aforeign object is present. If it is difficult to detect the foreignobject using the quality factor, the wireless power receiver may includeinformation on the reference peak frequency in a foreign objectdetection status packet and transmit the packet to the wireless powertransmitter, and the wireless power transmitter may detect the foreignobject further using information on the reference peak frequency,thereby improving foreign object detection capability.

In the ping phase 520, when the object is sensed, the transmitter wakesup the receiver and transmits a digital ping for identifying whether thedetected object is a wireless power receiver. In the ping phase 520,when a response signal to the digital ping, for example, a signalstrength packet, is not received from the receiver, the transmitter maytransition to the selection phase 510 again. In addition, in the pingphase 520, when a signal indicating that power transfer has beenterminated, that is, a charging termination packet, is received from thereceiver, the transmitter may transition to the selection phase 510.

If the ping phase 520 is terminated, the transmitter may transition tothe identification and configuration phase 530 for identifying thereceiver and collecting the configuration and status information of thereceiver.

In the identification and configuration phase 530, when an unexpectedpacket is received, when an expected packet is not received during apredetermined time (timeout), when a packet transmission error occurs,or when power transfer contract is not established (no power transfercontract), the transmitter may transition to the selection phase 510.

The transmitter may determine whether entry into the negotiation phase540 is necessary based on the negotiation field value of theconfiguration packet received in the identification and configurationphase 530.

Upon determining that negotiation is necessary, the transmitter maytransition to the negotiation phase 540 to perform a predetermined FODprocedure.

In contrast, upon determining that negotiation is not necessary, thetransmitter may immediately transition to the power transfer phase 560.

In the negotiation phase 540, the transmitter may receive a foreignobject detection (FOD) status packet including a reference qualityfactor value. Alternatively, an FOD status packet including a referencepeak frequency value may be received. Alternatively, a status packetincluding a reference quality factor value and a reference peakfrequency value may be received. At this time, the transmitter maydetermine a quality factor threshold value for FO detection based on thereference quality factor value.

Alternatively, the transmitter may determine a peak frequency thresholdvalue for FO detection based on the reference peak frequency value. Thetransmitter may detect whether an FO is present in the charging areausing the quality factor threshold value for FO detection and acurrently measured quality factor value (a quality factor value measuredbefore the ping phase) and control power transfer according to theresult of FO detection. For example, when the FO is detected, a negativeacknowledgement signal may be transmitted to the wireless power receiverin response to the FOD status packet. Therefore, power transfer may bestopped, without being limited thereto.

The transmitter may detect whether an FO is present in the charging areausing the peak frequency threshold value for FO detection and acurrently measured quality factor value (a quality factor value measuredbefore the ping phase) and control power transfer according to theresult of FO detection. For example, when the FO is detected, a negativeacknowledgement signal may be transmitted to the wireless power receiverin response to the FOD status packet. Therefore, power transfer may bestopped, without being limited thereto.

When the FO is detected, the transmitter may return to the selectionphase 510 when the receiver transmits an end-of-charge message. Incontrast, when the FO is not detected, the transmitter may end transmitpower negotiation and enter the power transfer phase 560 through thecalibration phase 550. Specifically, when the FO is not detected, thetransmitter may measure power loss at the reception end and thetransmission end, in order to determine the strength of the powerreceived by the reception end and to determine the strength of the powertransmitted by the transmission end in the calibration phase 550. Thatis, the transmitter may predict power loss based on a difference betweenthe transmission power of the transmission end and the reception powerof the reception end in the calibration phase 550. The transmitteraccording to one embodiment may calibrate the threshold value for FOdetection using the predicted power loss.

In the power transfer phase 560, when an unexpected packet is received,when an expected packet is not received during a predetermined time(timeout), when power transfer contract violation occurs or whencharging is terminated, the transmitter may transition to the selectionphase 510.

In addition, in the power transfer phase 560, if a power transfercontract needs to be reconfigured according to transmitter statuschange, etc., the transmitter may transition to the renegotiation phase570. At this time, when renegotiation is normally terminated, thetransmitter may return to the power transfer phase 560.

The power transfer contract may be configured based on the transmitterand receiver status information and characteristic information. Forexample, the transmitter status information may include information onthe maximum amount of transmittable power, information on the maximumnumber of receivable receivers, etc. and the receiver status informationmay include information on required power.

FIG. 3 is a block diagram illustrating the structure of a wireless powerreceiver according to an embodiment.

Referring to FIG. 3, the wireless power receiver 700 may include areception coil 710, a rectifier 720, a DC-to-DC converter 730, a load740, a sensing unit 750, a communication unit 760, and a main controller770. The communication unit 760 may include a demodulator 761 and amodulator 762.

Although the wireless power receiver 700 shown in the example of FIG. 3is shown as exchanging information with the wireless power transmitter600 through in-band communication, this is merely an embodiment and thecommunication unit 760 according to another embodiment may provideshort-range bidirectional communication through a frequency banddifferent from a frequency band used to transmit a wireless powersignal.

AC power received through the reception coil 710 may be transmitted tothe rectifier 720. The rectifier 720 may convert the AC power into DCpower and transmit the DC power to the DC-to-DC converter 730. TheDC-to-DC converter 730 may convert the strength of the DC power outputfrom the rectifier into a specific strength required by the load 740 andtransmit the converted power to the load 740.

The sensing unit 750 may measure the strength of the DC power outputfrom the rectifier 720 and provide the strength to the main controller770. In addition, the sensing unit 750 may measure the strength ofcurrent applied to the reception coil 710 according to wireless powerreception and transmit the measured result to the main controller 770.In addition, the sensing unit 750 may measure the internal temperatureof the wireless power receiver 700 and provide the measured temperaturevalue to the main controller 770.

For example, the main controller 770 may compare the strength of the DCpower output from the rectifier with a predetermined reference value anddetermine whether overvoltage occurs. Upon determining that overvoltageoccurs, a predetermined packet indicating that overvoltage has occurredmay be generated and transmitted to the modulator 762. The signalmodulated by the modulator 762 may be transmitted to the wireless powertransmitter 600 through the reception coil 710 or a separate coil (notshown).

For example, the main controller 770 may generate and transmit the FODstatus packet to the modulator 762 in the negotiation phase 540 of FIG.2. Here, the signal modulated by the modulator 762 may be transmitted tothe wireless power transmitter 600 through the reception coil 710 or aseparate coil (not shown).

If the strength of the DC power output from the rectifier is equal to orgreater than the predetermined reference value, the main controller 770may determine that a sensing signal is received and perform control totransmit a signal strength indicator corresponding to the sensing signalto the wireless power transmitter 600 through the modulator 762 uponreceiving the sensing signal. In another example, the demodulator 761may demodulate the AC power signal between the reception coil 710 andthe rectifier 720 or the DC power signal output from the rectifier 720,identify whether a sensing signal is received, and provide theidentified result to the main controller 770. At this time, the maincontroller 770 may perform control to transmit the signal strengthindicator corresponding to the sensing signal through the modulator 762.

FIG. 4 is a view illustrating a packet format according to anembodiment.

Referring to FIG. 4, the packet format 900 used for information exchangebetween the wireless power transfer end 10 and the wireless powerreception end 20 may include a preamble 910 field for acquiringsynchronization for demodulation of the corresponding packet andidentifying an accurate start bit of the corresponding packet, a header920 field for identifying the type of a message included in thecorresponding packet, a message 930 field for transmitting the content(or payload) of the corresponding packet, and a checksum 940 field foridentifying whether an error has occurred in the corresponding packet.

A packet reception end may identify the size of the message 930 includedin the corresponding packet based on the value of the header 920.

In addition, the header 920 may be defined for each step of the wirelesspower transfer procedure, and the value of the header 920 may be definedas the same value in different phases of the wireless power transmissionprocedure. For example, referring to FIG. 6, it should be noted that theheader value corresponding to end power transfer of the ping phase andend power transfer of the power transfer phase is 0x02.

The message 930 includes data to be transmitted by the transmission endof the corresponding packet. For example, the data included in themessage 930 field may be a report, a request, or a response, withoutbeing limited thereto.

The packet 900 according to another embodiment may further include atleast one of transmission end identification information for identifyingthe transmission end for transmitting the corresponding packet andreception end identification information for identifying the receptionend for receiving the corresponding packet. The transmission endidentification information and the reception end identification mayinclude IP address information, MAC address information, productidentification information, etc. However, the embodiment is not limitedthereto and information for distinguishing the reception end and thetransmission end in the wireless charging system may be included.

The packet 900 according to another embodiment may further includepredetermined group identification information for identifying areception group if the corresponding packet is received by a pluralityof apparatuses.

FIG. 5 is a view illustrating the types of packets transmitted from thewireless power receiver to the wireless power transmitter according toan embodiment.

Referring to FIG. 5, the packet transmitted from the wireless powerreceiver to the wireless power transmitter may include a signal strengthpacket for transmitting the strength information of a sensed pingsignal, a power transfer type (end power transfer) for requesting powertransfer end from the transmitter, a power control hold-off packet fortransferring information on a time until actual power is controlledafter a control error packet for control is received, a configurationpacket for transferring configuration information of the receiver, anidentification packet and an extended identification packet fortransmitting receiver identification information, a general requestpacket for transmitting a general request message, a specific requestpacket for transmitting a specific request message, an FOD status packetfor transmitting a reference quality factor value and/or a referencepeak frequency value for FO detection, a control error packet forcontrolling power transmitted by the transmitter, a renegotiation packetfor starting renegotiation, a 24-bit received power packet fortransmitting the strength information of the received power, and acharge status packet for transmitting the current charging statusinformation of the load.

The packets transmitted from the wireless power receiver to the wirelesspower transmitter may be transmitted using in-band communication usingthe same frequency band as the frequency band used to transmit wirelesspower.

Referring to FIG. 6, the wireless power transmitter 1100 may include apower supply 1101, a DC-to-DC converter 1110, an inverter 1120, aresonant circuit or a coil unit 1130, a measurement unit 1140, acommunication unit 1160, an alarm unit 1175, and a control unit orcontroller 1180.

The wireless power transmitter 1100 according to the present embodimentmay be mounted in a measurement apparatus for authentication of awireless power reception apparatus or a wireless power transmissionapparatus.

The resonant circuit 1130 may include a resonant capacitor 1131 and aninductor (or a transmission coil) 1132 to convert current into flux ofmagnetic force.

The communication unit 1160 may include at least one of a demodulator1161 and a modulator 1162.

The controller 1180 may perform in-band communication or out-of-bandcommunication with the wireless power receiver through the communicationunit 1160.

The power supply 1101 may receive DC power through an external powerterminal or a battery and transmit the DC power to the DC-to-DCconverter 1110. Here, the battery may be mounted in the wireless powertransmitter 110 and may be charged but is merely an embodiment. Thebattery may be connected to a predetermined cable of the power supply1101 of the wireless power transmitter 1100 in the form of an auxiliarybattery or an external battery.

The DC-to-DC converter 1110 may convert the strength of the DC powerreceived from the power supply 1101 into a specific strength of DC powerunder control of the controller 1180. For example, the DC-to-DCconverter 1110 may include a variable voltage generator capable ofadjusting the strength of the voltage, without being limited thereto.

The inverter 1120 may convert the converted DC power into AC power. Theinverter 1120 may convert the DC power signal input through control of aplurality of switches into an AC power signal and output the AC powersignal.

For example, the inverter 1120 may include a full bridge circuit.However, the embodiment is not limited thereto and the inverter mayinclude a half bridge circuit.

In another example, the inverter 1120 may include a half bridge circuitand a full bridge circuit. In this case, the controller 1180 maydynamically determine whether the inverter 1120 operates as a halfbridge or a full bridge.

The wireless power transmission apparatus according to one embodimentmay adaptively control the bridge mode of the inverter 1120 according tothe strength of the power required by the wireless power receptionapparatus.

Here, the bridge mode includes a half bridge mode and a full bridgemode.

For example, if the wireless power reception apparatus requests lowpower of 5 W, the controller 1180 may perform control such that theinverter 1120 is driven in the half bridge mode.

In contrast, if the wireless power reception apparatus requests highpower of 15 W, the controller 1180 may perform control such that theinverter is driven in the full bridge mode.

In another example, the wireless power transmission apparatus mayadaptively determine the bridge mode according to a sensed temperatureand drive the inverter 1120 in the determined bridge mode.

For example, if the temperature of the wireless power transmissionapparatus exceeds a predetermined reference value while wireless poweris transmitted using the half bridge mode, the controller 1180 mayperform control to deactivate the half bridge mode and activate the fullbridge mode. That is, the wireless power transmitter 1100 may increasethe voltage and decrease the strength of current flowing in the resonantcircuit 1130 through the full bridge circuit for transmission of powerhaving the same strength, thereby maintaining the internal temperatureof the wireless power transmission apparatus at a reference value orless. In general, the amount of heat generated in an electronic partmounted in the electronic apparatus may be more sensitive to thestrength of current than the strength of the voltage applied to theelectronic part.

In addition, the inverter 1120 may not only convert the DC power into ACpower but also change the strength of the AC power.

For example, the inverter 1120 may adjust the strength of the output ACpower by adjusting the frequency of a reference alternating currentsignal used to generate the AC power under control of the controller1180. To this end, the inverter 1120 may include a frequency oscillatorfor generating the reference alternating current signal having aspecific frequency. However, this is merely an example and the frequencyoscillator may be mounted independently of the inverter 1120 and mountedat one side of the wireless power transmitter 1100.

In another example, the wireless power transmitter 1100 may furtherinclude a gate driver (not shown) for controlling the switch provided inthe inverter 1120. In this case, the gate driver may receive at leastone pulse width modulation signal from the controller 1180 and controlthe switch of the inverter 1120 according to the received pulse widthmodulation signal. The controller 1180 may control the duty cycle, thatis, the duty rate, and phase of the pulse width modulation signal tocontrol the strength of the output power of the inverter 1120. Thecontroller 1180 may adaptively control the duty cycle and phase of thepulse width modulation signal based on the feedback signal received fromthe wireless power reception apparatus.

The measurement unit 1140 may measure at least one of a voltage, currentand impedance of the resonant capacitor 1131 according to the controlsignal of the controller 1180 to calculate the quality factor value ofthe resonant circuit 1130. At this time, the calculated quality factorvalue may be transmitted to the controller 1180, and the controller 1180may store the quality factor value received from the measurement unit1140 in a predetermined recording region.

Alternatively, the measurement unit 1140 may measure a voltage acrossthe resonant capacitor 1131 to measure a resonant frequency value. Atthis time, the resonant frequency may mean a frequency having a maximumquality factor value. At this time, the calculated resonant frequencyvalue may be transmitted to the controller 1180 and the controller 1180may store the resonant frequency value received from the measurementunit 1140 in a predetermined recording region.

In addition, the measurement unit 1140 may measure the quality factorvalue within the available frequency band in certain frequency units andtransmit the result of measurement to the controller 1180, under controlof the controller 1180.

In addition, the measurement unit 1140 may detect current I_coil flowingin the coil unit and a voltage applied to the coil unit and provide thecurrent and the voltage to the controller 1180. At this time, thecontroller 1180 may demodulate the signal based on the voltage orcurrent received from the measurement unit 1140.

For example, when an object is detected in the selection phase, thecontroller 1180 may temporarily stop power transfer and request, fromthe measurement unit 1140, measurement of the quality factor values at aplurality of frequencies within the operating frequency band beforeentering the ping phase. The controller 1180 may identify a frequencycorresponding to a largest value among the measured quality factorvalues and determine the identified frequency as a current peakfrequency.

When the FOD status packet is received from the demodulator 1161 in thenegotiation phase, the controller 1180 may determine a threshold value(or a threshold range) for determining whether a foreign object ispresent based on information included in the FOD status packet. Here,the method of determining the threshold value (or the threshold range)will become more apparent through the description of the followingdrawings.

The FOD status packet may include at least one of a reference qualityfactor value Q reference corresponding to the wireless power receiverand/or a reference peak frequency F_reference_peak value.

The controller 1180 may determine a foreign object detection referencefrequency based on the received reference peak frequency value.

The controller 1180 may compare the determined foreign object detectionreference frequency with a current peak frequency to detect a foreignobject.

For example, when the current peak frequency value is greater than theforeign object detection reference frequency value, the controller 1180may determine that a foreign object is present in the charging area.

The frequency value comparison of the above-described embodiments may beperformed after conversion into a value corrected in consideration of anerror range or the manufacturing characteristics of a wireless powertransmitter.

As shown in the experimental results of the following drawings, the peakfrequency having a maximum quality factor value when a foreign object isplaced in the charging area is greater than the peak frequency beforethe foreign object is placed.

In addition, as shown in the experimental results of the followingdrawings, it can be seen that the peak frequency may be changedaccording to a position of the wireless power receiver placed in thecharging area.

Accordingly, when the reference peak frequency received from thewireless power receiver is determined as the foreign object detectionreference frequency, the foreign object detection apparatus 1200 maymis-determine peak frequency change according to receiver positionchange as peak frequency change due to a foreign object placed in thecharging area. In order to solve this, the foreign object detectionreference frequency according to an embodiment may be determined byapplying a predetermined tolerance value corresponding to peak frequencychange according to receiver movement to the reference peak frequencyvalue. For example, if the tolerance value is 5 kHz, the foreign objectdetection reference peak frequency may be set to a value obtained byadding 5 kHz to the reference peak frequency.

Accordingly, the controller 1180 may determine whether the current peakfrequency value is greater or less than the foreign object detectionreference frequency value and determine whether the current peakfrequency is changed from the reference peak frequency due to movementof the receiver.

When the controller 1180 determines that the foreign object is present,the wireless power transmitter may transmit a negative acknowledgementsignal to the wireless power receiver in response to the FOD statuspacket. Therefore, the wireless power receiver may transmit anend-of-charge message to the wireless power transmitter. The wirelesspower transmitter may stop power transfer when the end-of-charge messageis received. As an additional embodiment, the alarm unit 1175 may becontrolled to output a predetermined warning alarm indicating that theforeign object has been detected. For example, the alarm unit 1175 mayinclude a beeper, an LED lamp, a vibration element, and a liquid crystaldisplay, without being limited thereto. Any alarm unit capable ofnotifying the user of foreign object detection may be used.

The reference quality factor value or the reference peak frequency valueincluded in the FOD status packet may be predetermined throughexperimentation on a specific wireless power transmitter (or ameasurement apparatus) designated for standard performance test andreceiver authentication and may be set in the wireless power receiver.

For example, the smallest value of the quality factor values measured incorrespondence with the wireless power receiver at a plurality ofdesignated positions in the charging area, for example, a charging padprovided on the wireless power transmitter or the measurement apparatus,may be determined as the reference quality factor value.

For example, the highest value of the peak frequency values measured incorrespondence with the wireless power receiver at a plurality ofdesignated positions in the charging area, for example, a charging padprovided on the wireless power transmitter or the measurement apparatus,may be determined as the reference quality factor value.

When the foreign object is detected in the negotiation phase, thecontroller 1180 may transmit a negative acknowledgement signal to thewireless power receiver in response to the FOD status packet. Therefore,the wireless power receiver may transmit an end-of-charge message to thewireless power transmitter. The wireless power transmitter may stoppower transfer and return to the selection phase, when the end-of-chargemessage is received.

As an additional embodiment, the controller 1180 may perform the foreignobject detection procedure again after returning to the selection phaseand determine whether the detected foreign object has been removed fromthe charging area. Upon determining that the foreign object has beenremoved, the controller 1180 may enter the power transfer phase andperform charging of the wireless power reception apparatus.

In addition, the controller 1180 may monitor whether a response signal,for example, a signal strength packet, is normally received in the pingphase. For example, the controller 1180 may calculate the number oftimes that the signal strength packet is not normally received afterdigital ping transmission.

In addition, the controller 1180 may monitor whether the identificationand configuration packet is normally received in the identification andconfiguration phase. For example, the controller 1180 may calculate thenumber of reception failures of the identification and configurationpacket.

Hereinafter, an example of determining reception failure of theidentification and configuration packet will be described.

For example, the controller 1180 may determine that reception of theidentification and configuration packet has failed when theidentification packet is not normally received within a predeterminedfirst time after the signal strength packet is normally received.

In another example, the controller 1180 may determine that reception ofthe identification and configuration packet has failed when all a seriesof identification packets is not sequentially received within apredetermined second time after the signal strength packet is normallyreceived.

Hereinafter, for convenience of description, the number of packetreception failures in the ping phase and/or the identification andconfiguration phase is referred to as a communication error count.

For example, the controller 1180 may determine that a foreign object ispresent on a wireless power transmission path, when the current peakfrequency value is greater than the foreign object detection referencefrequency value and the communication error count exceeds apredetermined communication error reference value.

In contrast, the controller 1180 may determine that a foreign object isnot present on the wireless power transmission path, when the currentpeak frequency value is greater than the foreign object detectionreference frequency value but the communication error count is equal toor less than the predetermined communication error reference value.

FIG. 7 is a block diagram illustrating the structure of a foreign objectdetection apparatus according to another embodiment.

Referring to FIG. 7, the foreign object detection apparatus 1200 mayinclude a measurement unit 1210, a search unit 1220, a communicationunit 1230, a determination unit 1240, a detection unit 1250, an alarmunit 1260, a storage unit 1270, a transmission unit 1280 and acontroller 1290. It should be noted that the components of the foreignobject detection apparatus 1200 are not mandatory and more or fewercomponents may be included.

The transmission unit 1280 may include a DC-to-DC converter, aninverter, and a resonant circuit for wireless power transmission.

Upon detecting an object placed in the charging area in the selectionphase, the measurement unit 1210 may temporarily stop power transfer andmeasure the quality factor value at a predetermined reference operatingfrequency. Here, the quality factor value may be measured at a pluralityof frequencies determined within an available frequency band (or anoperating frequency band). For example, the available frequency band maybe 88 kHz to 151 kHz, but is merely an embodiment, and may be changedaccording to the design purposes of those skilled in the art and appliedwireless power transmission technology (or standard).

The search unit 1220 may search for a frequency having a maximum qualityfactor value, that is, a current peak frequency, based on the result ofmeasurement of the measurement unit 1210. The current peak frequencysearched by the search unit 1220 may be stored in a predeterminedrecording region of the storage unit 1270.

Referring to the experimental results of the following drawings, when aforeign object is placed in the charging area along with the wirelesspower receiver, the peak frequency having a maximum quality factor valuemay further increase as compared to the case where only the wirelesspower receiver is placed in the charging area.

The communication unit 1230 may demodulate a wireless signal and acquirevarious packets transmitted by the wireless power receiver as shown inFIG. 5. For example, the communication unit 1230 may acquire a signalstrength packet in the ping phase. In addition, the communication unit1230 may acquire an identification packet and a configuration packet inthe identification and configuration phase. In addition, thecommunication unit 1230 may acquire a foreign object detection (FOD)status packet in the negotiation phase. In addition, the communicationunit 1230 may receive a control error packet for power control, areceive power packet, etc. in the power transfer phase.

For example, the foreign object detection status packet may include atleast one of a reference quality factor value Q_reference or a referencepeak frequency value F_reference_peak.

The structure of the foreign object detection status packet will becomemore apparent through the description of FIG. 10.

The determination unit 1240 may determine the foreign object detectionreference frequency based on the reference peak frequency value includedin the foreign object detection status packet.

For example, the determination unit 1240 may calculate the foreignobject detection reference frequency by adding a predetermined firsttolerance value based on maximum peak frequency change according toreceiver movement to the reference peak frequency value.

In another example, the determination unit 1240 may calculate theforeign object detection reference frequency by adding a predeterminedsecond tolerance value based on maximum peak frequency change accordingto a difference between wireless power transmitter types to thereference peak frequency value.

In another example, the determination unit 1240 may determine the largervalue of the first tolerance value and the second tolerance value as thetolerance value and add the determined tolerance value to the referencepeak frequency value to calculate the foreign object detection referencefrequency.

The detection unit 1250 may compare the determined foreign objectdetection reference frequency with the current peak frequency to detecta foreign object placed on the wireless power transmission path.

For example, the detection unit 1250 may determine that a foreign objectis present in the charging area when the current peak frequency isgreater than the foreign object detection reference frequency (or theboundary value calculated using the reference frequency).

As shown in the experimental results of FIG. 13, when a foreign objectis placed in the charging area, the value of the peak frequency having amaximum quality factor value becomes greater than the peak frequencybefore the foreign object is placed.

In addition, as shown in the experimental results of FIG. 13, it can beseen that the peak frequency is changed according to the position of thewireless power receiver placed in the charging area.

Accordingly, when the reference peak frequency received from thewireless power receiver is determined as the foreign object detectionreference frequency, the foreign object detection apparatus 1200 maymis-determine peak frequency change according to receiver positionchange as peak frequency change due to a foreign object placed in thecharging area. In order to solve this, the foreign object detectionreference frequency according to an embodiment may be determined inconsideration of the reference peak frequency value and a predeterminedtolerance value corresponding to peak frequency change according toreceiver movement. For example, if the tolerance value is 5 kHz, theforeign object detection reference peak frequency may be set to a sum ofthe reference peak frequency and 5 kHz.

However, according to the below-described experimental results, it canbe seen that increment (or increase ratio) of the peak frequency valueaccording to foreign object placement is greater than increment (ordeviation) of the peak frequency according to movement of the receiverin the charging area. Accordingly, the detection unit 1250 according toone embodiment may determine whether the current peak frequency value isgreater or less than the foreign object detection reference frequencyvalue and accurately determine whether the current peak frequency hasbeen changed from the reference peak frequency due to the foreign objector due to movement of the receiver.

In addition, according to the below-described experimental results, itcan be seen that increment (or increase ratio) of the peak frequencyvalue according to foreign object placement is greater than increment(or deviation) of the peak frequency according to the difference betweenthe types of the wireless power transmitters. Accordingly, the detectionunit 1250 according to one embodiment may determine whether the currentpeak frequency value is greater or less than the foreign objectdetection reference frequency value and accurately determine whether thecurrent peak frequency has been changed from the reference peakfrequency due to the foreign object or due to the difference between thetransmitters.

Upon determining that the foreign object is present on the wirelesspower transmission path, the detection unit 1250 may stop power transferand control the alarm unit 1260 to output a predetermined warning alarmindicating that the foreign object has been detected. For example, thealarm unit 1160 may include a beeper, an LED lamp, a vibration element,and a liquid crystal display, without being limited thereto. Any alarmunit capable of notifying the user of foreign object detection may beused.

The reference quality factor value included in the foreign objectdetection status packet may be predetermined through experimentation ona specific wireless power transmitter (or a measurement apparatus)designated for standard performance test and receiver authentication andmay be set in the wireless power receiver. For example, the smallestvalue of the quality factor values measured in correspondence with thewireless power receiver at a plurality of designated positions in thecharging area, for example, a charging pad provided on the wirelesspower transmitter or the measurement apparatus, may be determined as thereference quality factor value.

When the foreign object is detected in the negotiation phase, thecontroller 1290 may transmit a negative acknowledgement signal to thewireless power receiver in response to the foreign object detectionstatus packet. Therefore, the wireless power receiver may transmit anend-of-charge message to the wireless power transmitter. The wirelesspower transmitter may stop power transfer and return to the selectionphase, when the end-of-charge message is received.

The controller 1290 may perform the foreign object detection procedureagain after returning to the selection phase and determine whether thedetected foreign object has been removed from the charging area. Upondetermining that the foreign object has been removed, the controller1290 may enter the power transfer phase and perform charging of thewireless power reception apparatus.

In addition, the controller 1290 may monitor whether a response signal,for example, a signal strength packet, is normally received in the pingphase. For example, the controller 1290 may monitor whether the signalstrength packet corresponding to the digital ping is normally receivedand calculate the number of times that the signal strength packet is notnormally received, that is, the communication error count.

In addition, the controller 1290 may monitor whether the identificationand configuration packet is normally received in the identification andconfiguration phase. Specifically, the controller 1180 may monitorwhether the identification and configuration packet is normally receivedand calculate the number of times that the identification andconfiguration packet is not normally received, that is, thecommunication error count.

For example, the controller 1290 may determine that reception of theidentification and configuration packet has failed, when theidentification packet is not normally received within a predeterminedfirst time after the signal strength packet is normally received.

In another example, the controller 1290 may determine that reception ofthe identification and configuration packet has failed when a series ofidentification packets is not sequentially received within apredetermined second time after the signal strength packet is normallyreceived.

Hereinafter, for convenience of description, the number of packetreception failures in the ping phase and/or the identification andconfiguration phase is referred to as a communication error count.

For example, the controller 1290 may determine that a foreign object ispresent, when the foreign object detection reference frequency value isgreater than the current peak frequency value and the communicationerror count exceeds a predetermined communication error reference value.

In contrast, the controller 1290 may determine that a foreign object isnot present, when the foreign object detection reference frequency valueis greater than the current peak frequency value but the communicationerror count is equal to or less than the predetermined communicationerror reference value.

FIG. 8 is a state transition diagram illustrating a foreign objectdetection procedure of a foreign object detection apparatus according toan embodiment.

Referring to FIG. 8, when the object is detected in the selection phase1310, the wireless power transmitter may search for a frequency having amaximum quality factor value, that is, a current peak frequencyF_current_peak or a resonant frequency, within an available frequencyband before entering the ping phase 1320. The foreign object detectionapparatus may store information on the searched current peak frequencyin a predetermined recording region of the memory.

When entering the ping phase 1320, the foreign object detectionapparatus may transmit a predetermined power signal for identifying thewireless power receiver, for example, a digital ping.

When a response signal to the power signal transmitted in the ping phase1320, for example, a signal strength packet, is received, the wirelesspower transmitter may enter the identification and configuration phase1330 to identify the wireless power receiver and set variousconfiguration parameters necessary for wireless power transmission tothe identified wireless power receiver. In addition, the foreign objectdetection apparatus may determine whether the wireless power receiveridentified in the identification and configuration phase 1330 is capableof receiving power.

When identification and configuration of the wireless power receivernormally ends, the wireless power receiver may enter the negotiationphase 1340 to perform a foreign object detection procedure.

The foreign object detection procedure may be performed through thefollowing three steps.

In step 1, the wireless power transmitter may receive at least oneforeign object detection status packet from the identified wirelesspower receiver. Here, the foreign object detection status packet mayinclude at least one of information on the reference peak frequencyvalue or information on the reference quality factor value measured atthe reference peak frequency.

In step 2, the wireless power transmitter may determine a foreign objectdetection reference frequency for determining whether a foreign objectis present based on the received reference peak frequency value. Here,the foreign object detection reference frequency may be determined inconsideration of a tolerance value of peak frequency change according tomovement of the receiver in the charging area in addition to thereference peak frequency value. For example, if the tolerance value is 5kHz, the foreign object detection reference peak frequency may bedetermined by a sum of the reference peak frequency and 5 kHz.

In step 3, the wireless power transmitter may compare the current peakfrequency with the foreign object detection reference frequency todetermine whether a foreign object is present on the wireless powertransmission path. The foreign object detection apparatus may determinethat the foreign object is present when the current peak frequency isgreater than the foreign object detection reference frequency. Incontrast, the foreign object detection apparatus may determine that theforeign object is not present when the current peak frequency is lessthan the foreign object detection reference frequency.

Upon determining that the foreign object is present, the wireless powertransmitter may transmit a negative acknowledgement signal to thewireless power receiver in response to the FOD status packet. Therefore,the wireless power receiver may transmit an end-of-charge message to thewireless power transmitter. The wireless power transmitter may stoppower transfer and return to the selection phase 1310, when theend-of-charge message is received. At this time, the wireless powertransmitter may output a predetermined warning alarm message indicatingthat the foreign object has been detected using an alarm unit.

In another example, when the foreign object is detected, a predeterminedwarning alarm message indicating that the foreign object has beendetected may be transmitted to the wireless power receiver beforeentering the selection phase 1310. Subsequently, the wireless powerreceiver may transmit a message for requesting power transfer end, forexample, End of Power Transfer Packet, to the wireless power transmitteraccording to the warning alarm message.

In contrast, upon determining that the foreign object is not present,the wireless power transmitter may enter the power transfer phase 1350and perform wireless charging with respect to the wireless powerreceiver.

FIG. 9 is a state transition diagram illustrating a foreign objectdetection procedure of a foreign object detection apparatus according toanother embodiment.

Referring to FIG. 9, when the object is detected in the selection phase1410, the foreign object detection apparatus may search for a frequencyhaving a largest quality factor value, that is, a current peak frequencyF_current_peak, in the available frequency band before entering the pingphase 1420.

Upon entering the ping phase 1420, the foreign object detectionapparatus may transmit a predetermined power signal for identifying thewireless power receiver, for example, a digital ping. At this time, theforeign object detection apparatus may monitor the reception state of aresponse signal corresponding to the power signal, for example, a signalstrength packet, and collect communication error statistical data.

When the response signal is not normally received, the foreign objectdetection apparatus may repeatedly transmit the power signal and collectstatistical data on the number of reception failures of the responsesignal. When the number of reception failures of the response signalexceeds a predetermined reference value, the foreign object detectionapparatus may enter the selection phase 1410 or end all power transferfor a predetermined time.

When the response signal to the power signal transmitted in the pingphase 1420 is normally received, the foreign object detection apparatusmay enter the identification and configuration phase 1430 to identifythe wireless power receiver and set various configuration parametersnecessary for wireless power transmission to the identified wirelesspower receiver.

In addition, the foreign object detection apparatus may determinewhether the wireless power receiver identified in the identification andconfiguration phase 1430 is capable of receiving power.

The foreign object detection apparatus may return to the selection phase1410 when the identification and configuration packet is not normallyreceived. At this time, the foreign object detection apparatus maycollect statistical data on the number of reception failures of theidentification and configuration packet.

When the number of reception failures of the identification andconfiguration packet exceeds a predetermined reference value, theforeign object detection apparatus may enter the selection phase 1410 orend all power transfer for a predetermined time.

When the number of reception failures of the response signal and/or theidentification and configuration packet exceeds a predeterminedreference value, transfer of the power signal, that is, the power signalincluding the analog ping transmitted in the selection phase 1410, isinterrupted for a predetermined time, thereby minimizing unnecessarypower waste. If the number of times of interrupting power exceeds apredetermined reference value, the foreign object detection apparatusmay output a predetermined warning alarm indicating that the objectplaced in the charging area needs to be removed.

For example, the foreign object detection apparatus may manage thecumulative total of the number of reception failures of the responsesignal in the ping phase 1420 and the number of reception failures ofthe identification and configuration packet in the identification andconfiguration phase 1430 as the communication error count.

When the identification and configuration of the wireless power receivernormally ends, the foreign object detection apparatus may enter thenegotiation phase 1440 to perform the foreign object detectionprocedure.

The foreign object detection procedure may be performed through thefollowing four steps.

In step 1, the foreign object detection apparatus may receive at leastone foreign object detection status packet from the identified wirelesspower receiver. Here, the foreign object detection status packet mayinclude at least one of information on the reference peak frequency andinformation on the reference quality factor value measured at thereference peak frequency.

In step 2, the foreign object detection apparatus may determine aforeign object detection reference frequency for determining whether aforeign object is present based on the received reference peak frequencyvalue. Here, the foreign object detection reference frequency may bedetermined in consideration of a tolerance value of peak frequencychange according to movement of the receiver in the charging area inaddition to the reference peak frequency value. For example, if thetolerance value is 5 kHz, the foreign object detection reference peakfrequency may be determined by a sum of the reference peak frequency and5 kHz.

In step 3, the foreign object detection apparatus may compare thecurrent peak frequency value with the foreign object detection referencefrequency value.

In step 4, when the foreign object detection reference frequency valueis greater than the current peak frequency value as the result ofcomparison, the foreign object detection apparatus may determine whetherthe communication error count exceeds a predetermined communicationerror reference value.

Upon determining that the communication error count exceeds thepredetermined communication error reference value, the foreign objectdetection apparatus may determine that the foreign object is present onthe wireless power transmission path. Upon determining that the foreignobject is present, the foreign object detection apparatus may endwireless charging and return to the selection phase 1410. At this time,the foreign object detection apparatus may output a predeterminedwarning alarm message indicating that the foreign object has beendetected using an internal alarm unit. In another example, when theforeign object is detected, the foreign object detection apparatus maytransmit a predetermined warning alarm message indicating that theforeign object has been detected to the wireless power receiver beforeentering the selection phase 1410. Subsequently, the wireless powerreceiver may transmit a message for requesting power transfer end, forexample, End of Power Transfer Packet, to the wireless power transmitteraccording to the warning alarm message.

In contrast, upon determining that foreign object is not present, theforeign object detection apparatus may enter the power transfer phase1450 to perform wireless charging with respect to the wireless powerreceiver.

FIG. 10 is a view illustrating the structure of an FOD status packetmessage according to one embodiment.

Referring to FIG. 10, the FOD status packet message 1500 may have alength of 2 bytes, and include a first data 1501 field having a lengthof 6 bits, a mode 1502 field having a length of 2 bits and a second data(reference quality factor value) 1503 field having a length of 1 byte.

For example, in the foreign object detection status packet message 1500,as denoted by reference numeral 1504, if the mode 1502 field is set to“00”, all bits of the first data 1501 field are recorded with 0 andinformation corresponding to a reference quality factor value measuredand determined in a state in which the wireless power receiver ispowered off may be recorded in the second data 1503 field.

If the mode 1502 field is set to a binary value of “01”, all bits of thefirst data 1501 field may be recorded with 0 and informationcorresponding to a reference peak frequency value may be recorded in thereference value 1503 field.

Here, the reference peak frequency value may mean a frequency having alargest quality factor value within an available frequency band in astate in which only the wireless power receiver is placed in thecharging area. In addition, the reference peak frequency value is avalue measured and determined on a designated specific measurementapparatus (or a specific wireless power transmitter) designated forauthentication of the wireless power receiver.

In another example, in the foreign object detection status packetmessage 1500, as denoted by reference numeral 1505, if the mode 1502field is set to “00”, information corresponding to the reference peakfrequency value may be recorded in the first data 1501 field andinformation corresponding to a reference quality factor value measuredand determined in a state in which the wireless power receiver ispowered off may be recorded in the second data 1503 field.

The offset (or resolution) of the reference peak frequency valuerecorded in the first data 1501 field may be determined based on thesize of the data field and the size of the available (or operating)frequency band.

For example, since the size of the first data 1503 is 6 bits, the offsetmay have a value from 0 to 63. If the operating frequency bandwidth is128 kHz, the resolution of the reference peak frequency value may beobtained by dividing the available frequency bandwidth by the number offirst data 1501, that is, 128 kHz/64=2 kHz.

FIG. 11 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to an embodiment.

Referring to FIG. 11, the wireless power transmission apparatus maydetect an object placed in the charging area in the selection phase(S1610). When the object is detected, the wireless power transmissionapparatus search for a current peak frequency which is a frequencyhaving a maximum quality factor value among the quality factor valuesmeasured at a plurality of frequencies within the available frequencyband before entering the ping phase and store the current peak frequencyin a predetermined recording region (S1620). Here, the number offrequencies for measuring the quality factor value for search for thecurrent peak frequency within the available frequency band may bedetermined by a predetermined frequency offset. It should be noted thatthe frequency offset may be differently determined according to thedesign of those skilled in the art. In addition, the available frequencyband may vary according to the standard applied to the wireless chargingsystem.

In another embodiment, the wireless power transmission apparatus maydetect and store a current peak frequency having a largest coil voltage(or a largest voltage across a resonant capacitor) within apredetermined frequency region (S1620). The wireless power transmissionapparatus controls an operating frequency to sense a (frequency sweep)coil voltage (or a voltage across a resonant capacitor). For example,the wireless power transmission apparatus may measure a coil voltage (ora voltage across a resonant capacitor) while sweeping an operatingfrequency from a low frequency to a high frequency. The coil voltage (orthe voltage across the resonant capacitor) gradually increases and thendecreases while sweeping the frequency. At this time, when thedecreasing voltage is sensed, the wireless power transmission apparatusmay determine the operating frequency at that time as a resonantfrequency (a current peak frequency).

The wireless power transmission apparatus may determine a foreign objectdetection reference frequency based on the reference peak frequencyvalue (S1630), when the foreign object detection status packet includingthe reference peak frequency value is received in the negotiation phase.

The wireless power transmission apparatus may determine whether thecurrent peak frequency value exceeds the foreign object detectionreference frequency value (S1640).

Upon determining that the current peak frequency value exceeds theforeign object detection reference frequency value, the wireless powertransmission apparatus may determine that the foreign object is detected(S1650).

Upon determining that the current peak frequency value is less than theforeign object detection reference frequency value, the wireless powertransmission apparatus may determine that the foreign object is notdetected (S1660).

FIG. 12 is a flowchart illustrating a foreign object detection method ina wireless power transmission apparatus according to another embodiment.

Referring to FIG. 12, the wireless power transmission apparatus maydetect an object placed in the charging area in the selection phase(S1710). When the object is detected, the wireless power transmissionapparatus may temporarily stop power transfer before entering the pingphase, search for a current peak frequency which is a frequency having amaximum quality factor value among the quality factor values measured ata plurality of frequencies within the available frequency band, andstore the current peak frequency in a predetermined recording region(S1720). Here, the number of frequencies for measuring the qualityfactor value for search for the current peak frequency within theavailable frequency band may be determined by a predetermined frequencyoffset. It should be noted that the frequency offset may be differentlydetermined according to the design of those skilled in the art. Inaddition, the available frequency band may vary according to thestandard applied to the wireless charging system.

When the current peak frequency is searched, the wireless powertransmission apparatus may collect the statistical data of thecommunication error count (S1730). Here, the statistical data may becollected in at least one of the ping phase or the identification andconfiguration phase.

For example, the wireless power transmission apparatus may transmit adigital ping in order to identify the receiver in the ping phase. Thewireless power transmission apparatus may monitor whether the signalstrength packet as the response signal corresponding to the digital pingin the ping phase is normally received and calculate a firstcommunication error count corresponding to the ping phase.

In another example, when the signal strength packet is normally receivedin the ping phase, the wireless power transmission apparatus may enterthe identification and configuration phase and monitor the receptionstate of the identification packet and the configuration packet. At thistime, the wireless power transmission apparatus may calculate a secondcommunication error count corresponding to the identification andconfiguration phase.

Of course, the wireless power transmission apparatus may calculate athird communication error count which is a sum of the firstcommunication error count and the second communication error count.

When the foreign object detection status packet including the referencepeak frequency value is received in the negotiation phase, the wirelesspower transmission apparatus may determine the foreign object detectionreference frequency based on the reference peak frequency value (51740).

The wireless power transmission apparatus may check whether the currentpeak frequency value exceeds the foreign object detection referencefrequency value (51750).

Upon determining that the current peak frequency value exceeds theforeign object detection reference frequency value, the wireless powertransmission apparatus may check whether the communication error countexceeds a predetermined communication error reference value (51760).Here, the communication error count may be any one of the firstcommunication error count and the second communication error count.

Upon determining that the communication error count exceeds thepredetermined communication error reference value in step 1760, thewireless power transmission apparatus may determine that the foreignobject is detected (S1770).

Upon determining that the communication error count is less than thepredetermined communication error reference value, the wireless powertransmission apparatus may determine that the foreign object is notdetected (S1780).

Of course, upon determining that the current peak frequency value isless than or equal to the foreign object detection reference frequencyvalue in step 1750, the wireless power transmission apparatus maydetermine that the foreign object is not detected.

Accordingly, in the present embodiment, since whether the foreign objectis present is determined based on a difference between the referencepeak frequency stored in the wireless power receiver and the currentpeak frequency measured in the wireless power transmitter, it ispossible to more accurately detect the foreign object.

FIG. 13 is an experimental result graph showing change in quality factorvalue and peak frequency according to placement of a foreign object in awireless charging system according to an embodiment.

Referring to FIG. 13, when a first receiver and a foreign object areplaced in the charging area, the peak frequency is greater than that ofthe case where only the first receiver is placed in the charging area byΔf. Hereinafter, for convenience of description, Δf is referred to as apeak frequency shift value. In contrast, it can be seen that the qualityfactor value measured at the peak frequency corresponding to the statein which the first receiver and the foreign object are placed in thecharging area, that is, the current peak frequency, is less than thequality factor value measured at the peak frequency corresponding to thestate in which only the first receiver is placed, that is, the referencepeak frequency, by ΔQ. Hereinafter, for convenience of description, ΔQis referred to as a quality factor shift value.

As shown in FIG. 13, results similar to the experimental result of thefirst receiver are obtained with respect to the remaining second tofourth receivers.

The foreign object detection apparatus according to an embodiment maycalibrate the reference measurement quality factor value based on thepeak frequency shift value and the quality factor shift value. Forexample, as the sum of the peak frequency shift value and the qualityfactor shift value increases, the calibration ratio of the referencequality factor value may increase.

In general, in the case of a wireless charging system, a resonantphenomenon occurs at a peak frequency having a maximum quality factorvalue and power efficiency is maximized.

FIG. 14 is an experimental result table illustrating a peak frequency ofeach receiver type and change in peak frequency according to placementof a foreign object according to an embodiment.

Referring to FIG. 14, it can be seen that the peak frequency 1910acquired in the state in which only the wireless power receiver isplaced in the charging area and the quality factor value 1920 measuredat the peak frequency may have different values according to the type ofthe receiver.

In particular, referring to reference numerals 1910 and 1930, it can beseen that the peak frequency 1903 when not only the wireless powerreceiver but also the foreign object is placed in the charging area isgreater than the peak frequency 1910 when only the wireless powerreceiver is placed.

In addition, referring to reference numerals 1920 and 1940, it can beseen that the quality factor value measured when the receiver and theforeign object are placed in the charging area is less than the qualityfactor value frequency when only the receiver is placed.

In addition, referring to reference numeral 1950, the peak frequency isdecreased but the quality factor value is increased as the position ofthe foreign object placed in the charging area becomes farther from thecenter.

FIG. 15 is an experimental result table illustrating change in qualityfactor value and peak frequency according to movement of a wirelesspower receiver.

Referring to FIG. 15, change in peak frequency and change in qualityfactor value of each of first to third receivers when the wireless powerreceiver is moved from the center of the charging bed at an interval of5 mm in an up/down/left/right direction is shown. As shown in FIG. 16,it can be seen that maximum change in peak frequency according tomovement of the receiver on the charging bed is less than 5 kHz.

FIG. 16 is an experimental result showing change in peak frequencyaccording to the type of a wireless power transmitter andpresence/absence of a foreign object.

As shown in FIG. 16, it is characterized in that change in peakfrequency according to the type of the wireless power transmittercorresponding to each wireless power receiver is relatively less thanchange in peak frequency according to presence/absence of the foreignobject within a specific wireless power transmitter.

In the present embodiment, based on the above characteristics, when theobject is detected, the wireless power transmitter may measure thequality factor value within the available frequency band and search forthe peak frequency. At this time, the wireless power transmitter maycompare the searched peak frequency with the foreign object detectionreference frequency determined based on the reference peak frequency andidentify whether the peak frequency has been changed due to the foreignobject or a difference between the types of the wireless powertransmitters.

Accordingly, in the present embodiment, since presence/absence of theforeign object is determined based on the difference between thereference peak frequency stored in the wireless power receiver and thecurrent peak frequency actually measured in the wireless powertransmitter, it is possible to more accurately detect the foreignobject.

The wireless power transmitter according to the present embodiment maydetermine the foreign object detection reference frequency fordetermining whether the foreign object is present based on the referencepeak frequency value acquired from the wireless power receiver.

For example, the foreign object detection reference frequency may bedetermined in consideration of the reference peak frequency value and atolerance value corresponding to peak frequency change according to thedifference between the types of the wireless power transmitters. Forexample, if maximum peak frequency change according to the differencebetween the types of the wireless power transmitters is 5 kHz, theforeign object detection reference frequency may be set to a sum of thereference peak frequency value and 5 kHz.

In another example, the wireless power transmitter according to thepresent embodiment may determine the larger value of maximum peakfrequency change according to movement of the receiver in the chargingarea and maximum peak frequency change according to the differencebetween the types of the wireless power transmitters as a tolerancevalue. At this time, the foreign object detection reference frequencymay be set to a sum of the reference peak frequency value and thedetermined tolerance value.

The method according to the foregoing embodiments may be implemented ascode that can be written to a computer-readable recording medium and canthus be read by a computer. Examples of the computer-readable recordingmedium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk,an optical data storage, and a carrier wave (e.g., data transmissionover the Internet).

The computer-readable recording medium can be distributed over aplurality of computer systems connected to a network so thatcomputer-readable code is written thereto and executed therefrom in adecentralized manner. Functional programs, code, and code segmentsneeded to realize the embodiments herein can be construed by one ofordinary skill in the art.

Those skilled in the art will appreciate that the disclosure may becarried out in other specific ways than those set forth herein withoutdeparting from the spirit and essential characteristics of thedisclosure.

The above exemplary embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the disclosureshould be determined by the appended claims and their legal equivalents,not by the above description, and all changes coming within the meaningand equivalency range of the appended claims are intended to be embracedtherein.

INDUSTRIAL APPLICABILITY

Embodiments are applicable to a wireless power charging apparatus andare particularly applicable to a foreign object detection apparatus fordetecting a foreign object placed in a charging area and a wirelesspower transmission apparatus having a foreign object detection function.

1. A foreign object detection method of a wireless power transmitter,the foreign object detection method comprising: detecting an objectplaced in a charging area to measure a peak frequency having a maximumquality factor value; receiving a foreign object detection status packetincluding a reference peak frequency from a wireless power receiver;determining a frequency for detecting a foreign object based on thereference peak frequency; and comparing the peak frequency with thedetermined frequency to determine whether a foreign object is present.2. The foreign object detection method according to claim 1, wherein thedetermining of the frequency for detecting the foreign object includesdetermining the frequency for detecting the foreign object by a sum ofthe reference peak frequency and a tolerance.
 3. The foreign objectdetection method according to claim 1, wherein, when the peak frequencyis greater than the frequency for detecting the foreign object, adetermination is made that the foreign object is present.
 4. The foreignobject detection method according to claim 1, wherein the wireless powertransmitter measures the peak frequency before the wireless powerreceiver receives a ping signal.
 5. The foreign object detection methodaccording to claim 1, wherein the reference peak frequency has a maximumquality factor value within an available frequency band in a state inwhich only the wireless power receiver is placed in the charging area.6. The foreign object detection method according to claim 1, wherein theforeign object detection status packet further includes modeinformation, and the wireless power transmitter identifies the referencepeak frequency included in the foreign object detection status packetbased on the mode information.
 7. A foreign object detection apparatusfor detecting a foreign object placed in a charging area, the foreignobject detection apparatus comprising: a coil unit including an inductorand a resonant capacitor and configured to convert current into flux ofmagnetic force; an inverter configured to receive and convert directcurrent (DC) power into alternating current (AC) power and to transmitthe AC power to the coil unit; and a controller configured to control afrequency of the AC power output from the inverter and to demodulate asignal using a voltage or current of the coil unit, wherein thecontroller is configured to: detect an object placed in the chargingarea to measure a peak frequency having a maximum quality factor value,receive a foreign object detection status packet including a referencepeak frequency from a wireless power receiver, determine a frequency fordetecting a foreign object based on the reference peak frequency, andcompare the peak frequency with the determined frequency to determinewhether a foreign object is present.
 8. The foreign object detectionapparatus according to claim 7, wherein the controller determines thefrequency for detecting the foreign object by a sum of the referencepeak frequency and a tolerance.
 9. The foreign object detectionapparatus according to claim 7, wherein the controller measures the peakfrequency before the wireless power receiver receives a ping signal. 10.The foreign object detection apparatus according to claim 7, wherein thereference peak frequency corresponds to a maximum quality factor valuewithin an available frequency band in a state in which only the wirelesspower receiver is placed in the charging area.